Method and apparatus for reducing defibrillation threshold

ABSTRACT

An antitachyarrhythmia system uses vagal nerve stimulation in combination with one or more additional techniques to lower the defibrillation threshold (DFT). Examples of such additional techniques include using electrical shock waveforms each including a plurality of pulses and using defibrillation electrode configurations each including an electrode placed in the coronary sinus or coronary vein.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of co-pending, commonlyassigned, U.S. patent application Ser. No. 11/538,488, filed on Oct. 4,2006 and is related to co-pending, commonly assigned, U.S. patentapplication Ser. No. 11/275,943, filed on Feb. 6, 2006, which is acontinuation of U.S. patent Ser. No. 10/629,343, filed on Jul. 28, 2003,now abandoned, which is a continuation of U.S. patent Ser. No.10/118,603, filed on Apr. 8, 2002, now abandoned, which is a division ofU.S. patent application Ser. No. 09/448,648, now abandoned, which arehereby incorporated by reference in their entirety.

FIELD

This application relates generally to medical devices and, moreparticularly, to systems, devices and methods for providingneurally-mediated anti-arrhythmic therapy.

BACKGROUND

The heart is the center of a person's circulatory system. The leftportions of the heart draw oxygenated blood from the lungs and pump itto the organs of the body to provide the organs with their metabolicneeds for oxygen. The right portions of the heart draw deoxygenatedblood from the body organs and pump it to the lungs where the blood getsoxygenated. Contractions of the myocardium provide these pumpingfunctions. In a normal heart, the sinoatrial node, the heart's naturalpacemaker, generates electrical impulses that propagate through anelectrical conduction system to various regions of the heart to excitethe myocardial tissues of these regions. Coordinated delays in thepropagations of the electrical impulses in a normal electricalconduction system cause the various portions of the heart to contract insynchrony, which efficiently pumps the blood. Blocked or abnormalelectrical conduction or deteriorated myocardial tissue causesdysynchronous contraction of the heart, resulting in poor hemodynamicperformance, including a diminished blood supply to the heart and therest of the body. Heart failure occurs when the heart fails to pumpenough blood to meet the body's metabolic needs.

Tachyarrhythmias are abnormal heart rhythms characterized by a rapidheart rate. Examples of tachyarrhythmias include supraventriculartachycardias (SVT's) such as atrial tachycardia (AT), and atrialfibrillation (AF), and the more dangerous ventricular tachyarrhythmiaswhich include ventricular tachycardia (VT) and ventricular fibrillation(VF). Abnormal ventricular rhythms occur when re-entry of a depolarizingwavefront in areas of the ventricular myocardium with differentconduction characteristics becomes self-sustaining or when an excitatoryfocus in the ventricle usurps control of the heart rate from thesinoatrial node. The result is rapid and ineffective contraction of theventricles out of electromechanical synchrony with the atria. Manyabnormal ventricular rhythms exhibit an abnormal QRS complex in anelectrocardiogram because the depolarization spreads from the excitatoryfocus or point of re-entry directly into the myocardium rather thanthrough the normal ventricular conduction system. Ventriculartachycardia is typically characterized by distorted QRS complexes thatoccur at a rapid rate, while ventricular fibrillation is diagnosed whenthe ventricle depolarizes in a chaotic fashion with no identifiable QRScomplexes. Both ventricular tachycardia and ventricular fibrillation arehemodynamically compromising, and both can be life-threatening.Ventricular fibrillation, however, causes circulatory arrest withinseconds and is the most common cause of sudden cardiac death.

Cardioversion, an electrical shock delivered to the heart synchronouslywith the QRS complex, and defibrillation, an electrical shock deliveredwithout synchronization to the QRS complex, can be used to terminatemost tachyarrhythmias. Cardioversion and defibrillation are referredgenerally herein as antitachycardia shocks. The electric shockterminates the tachyarrhythmia by simultaneously depolarizing themyocardium and rendering it refractory. A class of cardiac rhythmmanagement (CRM) devices known as an implantable cardioverterdefibrillator (ICD) provides this kind of therapy by delivering a shockpulse to the heart when the device detects tachyarrhythmias. One type ofICD is a subcutaneous ICD. However, the defibrillation threshold (DFT)for a subcutaneous ICD is significantly elevated as compared to anintracardiac ICD. Because the energy required for each electrical shockis a significant factor determining battery life, and hence thelongevity, of the ICD, reduction of DFT is generally desired.

SUMMARY

An antitachyarrhythmia system uses vagal nerve stimulation incombination with one or more additional techniques to lower thedefibrillation threshold (DFT). Examples of such additional techniquesinclude using electrical shock waveforms each including a plurality ofpulses and using defibrillation electrode configurations each includingan electrode placed in the coronary sinus or coronary vein.

In one embodiment, an antitachyarrhythmia system includes a sensor, avagal nerve stimulator, defibrillation electrodes, and a defibrillator.The sensor detects a cardiac activity indicated for a defibrillationshock. The vagal nerve stimulator delivers vagal nerve stimulation tolower a defibrillation threshold in preparation for delivering thedefibrillation shock. The defibrillator delivers the defibrillationshock to the heart through the defibrillation electrodes, which includeat least one left ventricular (LV) electrode configured to be placed ina coronary sinus or coronary vein.

In one embodiment, a method for defibrillating a heart is provided. Acardiac activity indicated for a defibrillation shock is detected.Neural stimulation is applied to lower a defibrillation threshold inpreparation for the defibrillation shock. The defibrillation shock isdelivered using defibrillation electrodes including at least one LVelectrode placed in the coronary sinus or coronary vein.

This Summary is an overview of some of the teachings of the presentapplication and not intended to be an exclusive or exhaustive treatmentof the present subject matter. Further details about the present subjectmatter are found in the detailed description and appended claims. Otheraspects will be apparent to persons skilled in the art upon reading andunderstanding the following detailed description and viewing thedrawings that form a part thereof, each of which are not to be taken ina limiting sense. The scope of the present invention is defined by theappended claims and their equivalents.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a method according to various embodiments.

FIG. 2 illustrates a timing diagram for an example of the methodillustrated in FIG. 1.

FIG. 3 illustrates an embodiment of implantable medical device (IMD)having a neural stimulation (NS) component and an implantablecardioverter defibrillator (ICD) component.

FIG. 4 illustrates an embodiment of a microprocessor-based implantabledevice.

FIG. 5 illustrates a system embodiment including an implantable medicaldevice (IMD) and an external system or device.

FIG. 6 illustrates a system embodiment including an external device, animplantable neural stimulator (NS) device and an ICD device.

FIG. 7 illustrates an embodiment of a subcutaneous ICD with vagal nervestimulation.

FIG. 8 illustrates an embodiment of a system, including a subcutaneousICD and an implantable vagal nerve stimulator.

FIG. 9 illustrates an embodiment of a subcutaneous ICD with vagal nervestimulation.

FIG. 10 illustrates an embodiment of a system, including a subcutaneousICD and an implantable vagal nerve stimulator.

FIG. 11 illustrates an embodiment of a subcutaneous ICD with vagal nervestimulation.

FIG. 12 is a block diagram illustrating an embodiment of an externalsystem.

FIG. 13 illustrates an embodiment of an implantable medical device withan intracardiac lead system for delivering anti-arrhythmic therapy.

FIG. 14 illustrates an embodiment of an antitachycardia shock waveform.

FIG. 15 illustrates another embodiment of an antitachycardia shockwaveform.

DETAILED DESCRIPTION

The following detailed description of the present subject matter refersto the accompanying drawings which show, by way of illustration,specific aspects and embodiments in which the present subject matter maybe practiced. These embodiments are described in sufficient detail toenable those skilled in the art to practice the present subject matter.Other embodiments may be utilized and structural, logical, andelectrical changes may be made without departing from the scope of thepresent subject matter. References to “an”, “one”, or “various”embodiments in this disclosure are not necessarily to the sameembodiment, and such references contemplate more than one embodiment.The following detailed description is, therefore, not to be taken in alimiting sense, and the scope is defined only by the appended claims,along with the full scope of legal equivalents to which such claims areentitled.

An embodiment includes an implantable device adapted to providesubcutaneous anti-arrhythmic therapy, and to provide vagal stimulationto suppress and prevent tachyarrhythmias such as ventricular tachycardia(VT) or ventricular fibrillation (VF). The vagal stimulation can bedelivered intermittently or in response to sensed cardiac activity. Anembodiment of the device is adapted to respond to the detection of apotentially lethal tachyarrhythmia by delivering a subcutaneousantitachycardia shock, using synchronous vagal stimulation to lower thedefibrillation threshold (DFT) and enhance the efficacy of the shocktherapy. In various embodiments, the vagal stimulation significantlydecreases the DFT. The illustrated embodiment of the device includes animplantable pulse generator connected to a neural stimulation lead forvagal nerve stimulation. Vagal nerve stimulation is appliedintermittently, or in response to sensed cardiac activity predeterminedto be an indicator of potentially lethal tachyarrhythmias. An example ofsuch cardiac activity includes ST-segment elevation detected by wirelessECG. The subcutaneous device includes cardiac sensing and defibrillationcapabilities, and is adapted to detect tachyarrhythmias (such as VT/VF)and deliver an antitachycardia shock. In various embodiments, the deviceis adapted to deliver vagal nerve stimulation for a short period of time(e.g. 5-7 seconds) before applying the shock to lower the DFT andcounteract the inefficient shock delivery. Without the application ofvagal nerve stimulation, the DFT for a subcutaneous ICD is significantlyelevated as compared to an intracardiac ICD.

Various embodiments provide two implantable units that communicatewirelessly. One unit is placed in the pectoral region, and connected toa neural stimulation lead for vagal nerve stimulation. The other unit isplaced abdominally, and is responsible for cardiac sensing andcardioversion/defibrillation. In yet another embodiment, both units areinvolved in the cardiac sensing and/or cardioversion/defibrillation.

In an embodiment, vagal nerve stimulation is applied intermittently,such as ten seconds per minute, to prevent or abate progression ofcardiac disease development. Abating disease progression includespreventing the disease progression, or slowing down or reducing theintensity of the disease progression. In this case, the portion of thedevice responsible for cardiac sensing and cardioversion/defibrillationmonitors heart rate, and ensures that the heart rate does not fall belowunacceptable levels during vagal nerve stimulation. Other parameterssuch as blood pressure or minute ventilation can be used to assess theappropriateness of the neural stimulation. If heart rate falls below aprogrammable threshold, the device adjusts the stimulation (e.g.reducing the amount or turning off the vagal nerve stimulation).

A subcutaneous ICD with vagal stimulation capability can be used by anypatient at elevated risk for cardiac arrhythmias, and is believed to beparticularly beneficial for patients with moderately-elevated risk wholikely would not receive an ICD with intracardiac leads.

FIG. 1 illustrates a method according to various embodiments. Theillustrated method includes, at 101, detecting a predetermined cardiacactivity that has been indicated for an antitachycardia shock. Variousembodiments use the lead(s) of a subcutaneous ICD to detect thepredetermined cardiac activity. Various embodiments use electrodes on ahousing of a subcutaneously implanted device to detect the predeterminedcardiac activity. Various embodiments detect the predetermined cardiacactivity using a wireless EEG, which uses only electrodes on thesubcutaneously implanted device to detect the cardiac activity. Anexample of cardiac activity that has been indicated for anantitachycardia shock includes an elevated ST-segment. When it isdetermined that a shock should be applied, the process proceeds to 102to deliver vagal nerve stimulation in response to predetermined cardiacactivity to lower a defibrillation threshold (DFT) in preparation forthe antitachycardia shock. The vagal nerve stimulation can be deliveredthrough a lead to a vagus nerve in the cervical region. Variousembodiments use a lead with a nerve cuff electrode. Various embodimentsuse a transvascular lead fed into the internal jugular vein, or othervessel, to place at least one electrode proximate to a vagus nerve.Various embodiments use satellite electrodes in wireless communicationwith the subcutaneous defibrillator. The satellite electrodes can beself powered or can receive power wirelessly (e.g. through ultrasoundtransducers that recharge batteries or deliver power as needed for thestimulation). The shock is subcutaneously delivered, as illustrated at103.

Various embodiments apply prophylactic vagal nerve stimulation, asillustrated at 104. The prophylactic vagal nerve stimulation can beprovided as a therapy in addition to the nerve stimulation therapy tolower DFT, or can be provided as a therapy without the nerve stimulationtherapy to lower DFT. Modulation of the sympathetic and parasympatheticnervous system with neural stimulation has been shown to have positiveclinical benefits, such as protecting the myocardium from furtherremodeling and predisposition to fatal arrhythmias following amyocardial infarction. One example of a prophylactic vagal nervestimulation includes stimulation delivered to prevent ventricularfibrillation, such as may be applied after a myocardial infarction.Although the mechanisms are not completely understood at present,various studies have indicated that sympathetic hyperactivity oftentriggers life-threatening ventricular arrhythmias in the setting ofacute myocardial ischemia. Another example of a prophylactic vagal nervestimulation includes stimulation to prevent development of a cardiacdisease, such as anti-remodeling therapy.

FIG. 2 illustrates a timing diagram for an example of the methodillustrated in FIG. 1. As illustrated at 204, vagal nerve stimulation isdelivered intermittently as part of a prophylactic therapy. For example,the prophylactic therapy can be delivered on a schedule, such as 5minutes every hour. Arrow 201 illustrates a time when it is determinedthat it is appropriate or desirable to provide an antitachycardia shock.As illustrated at 202 vagal nerve stimulation is delivered to lower adefibrillation threshold (DFT) in anticipation of the shock. Variousembodiments deliver the neural stimulation to lower the DFT for lessthan one minute, various embodiments deliver the neural stimulation tolower the DFT for less than 15 seconds, and various embodiments deliverthe neural stimulation for a duration between approximately 5 seconds toapproximately 7 seconds. At 203, a subcutaneous defibrillator delivers adefibrillation shock after the DFT has been lowered. According tovarious embodiments, for example, the shock is delivered within oneminute after initiating the neural stimulation to lower the DFT. Variousembodiments deliver the shock within 20 seconds after initiating theneural stimulation to lower the DFT. Various embodiments deliver theshock within 10 seconds after initiating the neural stimulation to lowerthe DFT. The DFT will not be lowered if the neural stimulation isdelivered for too long of a duration before the defibrillation shock isdelivered. Various embodiments terminate the neural stimulationdelivered to lower DFT at or approximately when the shock is delivered.

FIG. 3 illustrates an IMD 305 having a neural stimulation (NS) component306 and ICD component 307, according to various embodiments of thepresent subject matter. The illustrated device includes a controller 308and memory 309. According to various embodiments, the controllerincludes hardware, software, or a combination of hardware and softwareto perform the neural stimulation and ICD functions. For example, theprogrammed therapy applications discussed in this disclosure are capableof being stored as computer-readable instructions embodied in memory andexecuted by a processor. According to various embodiments, thecontroller includes a processor to execute instructions embedded inmemory to perform the neural stimulation and ICD functions. An exampleof an ICD function includes antitachycardia shock therapy 310 such asmay include cardioversion or defibrillation, and examples of NSfunctions include parasympathetic stimulation and/or sympatheticinhibition to lower DFT 311, and parasympathetic stimulation and/orsympathetic inhibition as part of a prophylactic therapy 312 such as atherapy to prevent or diminish cardiac remodeling and/or a therapyapplied after a myocardial infarction to prevent ventricularfibrillation. The controller also executes instructions to detect atachyarrhythmia. The illustrated device further includes a transceiver313 and associated circuitry for use to communicate with a programmer oranother external or internal device. Various embodiments include atelemetry coil.

The ICD therapy section 307 includes components, under the control ofthe controller, to stimulate a heart and/or sense cardiac signals usingone or more electrodes. The illustrated ICD therapy section includes apulse generator 314 for use to provide an electrical signal throughelectrodes to stimulate a heart, and further includes sense circuitry315 to detect and process sensed cardiac signals. An interface 316 isgenerally illustrated for use to communicate between the controller 308and the pulse generator 314 and sense circuitry 315. The present subjectmatter is not limited to a particular number of electrode sites.

The NS therapy section 306 includes components, under the control of thecontroller, to stimulate a neural stimulation target, and in someembodiments sense parameters associated with nerve activity orsurrogates of nerve activity such as blood pressure and respiration.Three interfaces 317 are illustrated in the NS therapy section 306.However, the present subject matter is not limited to a particularnumber interfaces, or to any particular stimulating or sensingfunctions. Pulse generators 318 are used to provide electrical pulses toelectrode(s) or transducers for use to stimulate a neural stimulationtarget. According to various embodiments, the pulse generator includescircuitry to set, and in some embodiments change, the amplitude of thestimulation pulse, the frequency of the stimulation pulse, the burstfrequency of the pulse, and the morphology of the pulse such as a squarewave, triangle wave, sinusoidal wave, and waves with desired harmoniccomponents to mimic white noise or other signals. The controller cancontrol the initiation and termination of neural stimulation pulsetrains. Sense circuits 319 are used to detect and process signals from asensor, such as a sensor of nerve activity, blood pressure, respiration,and the like. The interfaces 317 are generally illustrated for use tocommunicate between the controller 308 and the pulse generator 318 andsense circuitry 319. Each interface, for example, may be used to controla separate lead. Various embodiments of the NS therapy section onlyinclude a pulse generator to stimulate or inhibit a neural target suchas a vagus nerve.

FIG. 4 shows a system diagram of an embodiment of a microprocessor-basedimplantable device, according to various embodiments. The controller ofthe device is a microprocessor 420 which communicates with a memory 421via a bidirectional data bus. The controller could be implemented byother types of logic circuitry (e.g., discrete components orprogrammable logic arrays) using a state machine type of design, but amicroprocessor-based system is preferable. As used herein, the term“circuitry” should be taken to refer to either discrete logic circuitryor to the programming of a microprocessor.

The illustrated device includes an ICD channel that includes electrodes422A, 422B and 422C, a sensing amplifier 423 for use in detectingcardiac activity using at least some of electrodes 422A, 422B and 422C,a shock pulse generator 424 for use in delivering an antitachycardiashock using at least some of electrodes 422A, 422B and 422C, and achannel interface 425 adapted to communicate bidirectionally withmicroprocessor 420. Although three electrodes are illustrated, the ICDchannel can use more or fewer electrodes, including at least one canelectrode 426. Wireless EEG, for example, can be detected using canelectrodes. The interface may include analog-to-digital converters fordigitizing sensing signal inputs from the sensing amplifiers andregisters that can be written to by the microprocessor in order tooutput pacing pulses, change the pacing pulse amplitude, and adjust thegain and threshold values for the sensing amplifiers. The sensingcircuitry detects a chamber sense, either an atrial sense or ventricularsense, when an electrogram signal (i.e., a voltage sensed by anelectrode representing cardiac electrical activity) generated by aparticular channel exceeds a specified detection threshold. Such sensescan be used to detect a cardiac rhythm that is indicated for adefibrillation shock. The intrinsic atrial and/or ventricular rates canbe measured by measuring the time intervals between atrial andventricular senses, respectively, and used to detect atrial andventricular tachyarrhythmias.

The illustrated electrodes are connected via conductors within the leadto a switching network 427 controlled by the microprocessor. Theswitching network is used to switch the electrodes to the input of asense amplifier in order to detect intrinsic cardiac activity and to theoutput of a pulse generator in order to deliver an antitachycardiashock. The switching network also enables the device to sense or shockeither in a bipolar mode using lead electrodes or in a unipolar modeusing a lead electrode and the device housing (can) 426 or an electrodeon another lead serving as a ground electrode.

Neural stimulation channels, identified as channels A and B, areincorporated into the device for delivering parasympathetic stimulationand/or sympathetic inhibition, where one channel includes a bipolar leadwith a first electrode 428A and a second electrode 429A, a pulsegenerator 430A, and a channel interface 431A, and the other channelincludes a bipolar lead with a first electrode 428B and a secondelectrode 429B, a pulse generator 430B, and a channel interface 431B.Other embodiments may use unipolar leads in which case the neuralstimulation pulses are referenced to the can or another electrode. Thepulse generator for each channel outputs a train of neural stimulationpulses which may be varied by the controller as to amplitude, frequency,duty-cycle, and the like. In this embodiment, each of the neuralstimulation channels uses a lead which can be subcutaneously tunneled orintravascularly disposed near an appropriate stimulation site. Othertypes of leads and/or electrodes may also be employed. A nerve cuffelectrode may be used around the cervical vagus nerve bundle to provideparasympathetic stimulation or around the aortic or carotid sinus nerveto provide sympathetic inhibition. In an embodiment, the leads of theneural stimulation electrodes are replaced by wireless links, and theelectrodes for providing parasympathetic stimulation and/or sympatheticinhibition are incorporated into satellite units.

The figure illustrates a telemetry interface 432 connected to themicroprocessor, which can be used to communicate with an externaldevice. The illustrated microprocessor 420 is capable of performingneural stimulation therapy routines and myocardial stimulation routines.Examples of NS therapy routines include an NS therapy to lower DFT, andan NS prophylactic therapy to prevent ventricular fibrillation after amyocardial infarction, or to prevent progression of cardiac disease.Examples of myocardial therapy routines include an antitachycardia shocktherapy such as cardioversion/defibrillation.

FIG. 5 illustrates a system 533 including an IMD 534 and an externalsystem or device 535, according to various embodiments of the presentsubject matter. Various embodiments of the IMD 534 include a combinationof NS and ICD functions. The external system 535 and the IMD 534 arecapable of wirelessly communicating data and instructions. In variousembodiments, for example, the external system and IMD use telemetrycoils to wirelessly communicate data and instructions. Thus, theprogrammer can be used to adjust the programmed therapy provided by theIMD, and the IMD can report device data (such as battery and leadresistance) and therapy data (such as sense and stimulation data) to theprogrammer using radio telemetry, for example. According to variousembodiments, the IMD stimulates a neural target to lower DFT inpreparation for a shock, and subcutaneously delivers the shock. Variousembodiments of the IMD also deliver a programmed neural stimulationtherapy as part of a prophylactic treatment for ventricular fibrillationor venticular remodeling.

The external system allows a user such as a physician or other caregiveror a patient to control the operation of IMD and obtain informationacquired by the IMD. In one embodiment, external system includes aprogrammer communicating with the IMD bi-directionally via a telemetrylink. In another embodiment, the external system is a patient managementsystem including an external device communicating with a remote devicethrough a telecommunication network. The external device is within thevicinity of the IMD and communicates with the IMD bi-directionally via atelemetry link. The remote device allows the user to monitor and treat apatient from a distant location. The patient monitoring system isfurther discussed below.

The telemetry link provides for data transmission from implantablemedical device to external system. This includes, for example,transmitting real-time physiological data acquired by the IMD,extracting physiological data acquired by and stored in IMD, extractingtherapy history data stored in implantable medical device, andextracting data indicating an operational status of the IMD (e.g.,battery status and lead impedance). Telemetry link also provides fordata transmission from external system to the IMD. This includes, forexample, programming the IMD to acquire physiological data, programmingthe IMD to perform at least one self-diagnostic test (such as for adevice operational status), and programming the IMD to deliver at leastone therapy.

FIG. 6 illustrates a system 633 including an external device 635, animplantable neural stimulator (NS) device 636 and a subcutaneous ICD637, according to various embodiments of the present subject matter.Various aspects involve a method for communicating between an NS deviceand the ICD. The illustrated NS device and the ICD are capable ofwirelessly communicating with each other, and the external system iscapable of wirelessly communicating with at least one of the NS and theCRM devices. For example, various embodiments use telemetry coils towirelessly communicate data and instructions to each other. In otherembodiments, communication of data and/or energy is by ultrasonic means.Rather than providing wireless communication between the NS and ICDdevices, various embodiments provide a communication cable or wire, suchas an intravenously-fed lead, for use to communicate between the NSdevice and the ICD device. In some embodiments, the external systemfunctions as a communication bridge between the NS and ICD devices.

FIG. 7 illustrates an embodiment of a subcutaneous ICD with vagal nervestimulation. The location of the device 734 is in a subcutaneous spacethat is developed during the implantation process, and the heart 738 isnot exposed during this process. The subcutaneous space is below thepatient's skin and over muscle tissue and the rib cage. The lead 739 ofthe subcutaneous electrode traverses in a subcutaneous path around thethorax terminating with its distal electrode lateral to the left scapulato deliver current between the can and electrode to the majority of theventricular myocardium. A distal electrode on the lead is a coilelectrode that is used for delivering the cardioversion/defibrillationenergy across the heart. The lead can also include sense electrodesspaced a distance to provide good QRS detection. The sensing of QRSwaves can be carried out using sense electrodes on the housing of thedevice 734 or using a combination of lead electrodes and housingelectrodes. The sensing vectors between electrodes can be adjusted toprovide the best detection of cardiac activity. When a shock is to beapplied, the sensing electrodes can be turned off and isolated fromdamage caused by the shock. A neural stimulation lead 740 extends fromthe device 734 to a vagal target. The neural stimulation lead 740 can betunneled subcutaneously to the vagus nerve, or can be transvascularlyfed to the internal jugular vein adjacent to the vagus nerve. Satelliteelectrodes may be used to deliver neural stimulation.

FIG. 8 illustrates an embodiment of a system, including a subcutaneousICD 837 and an implantable vagal nerve stimulator 836. The ICD 837 has asubcutaneous lead 839 similar to the lead 739 described with respect toFIG. 7. A separate vagal nerve stimulator 836 includes a neuralstimulation lead 840, which can be tunneled subcutaneously to the vagusnerve, or can be transvascularly fed to the internal jugular veinadjacent to the vagus nerve. The ICD and nerve stimulator are adapted tocommunicate with each other. The illustrated system illustrates wirelesscommunication between the devices, such as may be achieved usingultrasound or radiofrequency signals. A subcutaneously tunneled tethercan connect the two implanted devices, and communication and/or powercan be provided through the tether. Thus, the neural stimulation tolower the DFT can be coordinated with the delivery of the subcutaneousdefibrillation.

FIG. 9 illustrates an embodiment of a subcutaneous ICD with vagal nervestimulation. In the illustrated embodiment, there are two subcutaneousleads 939A and 939B connected to the ICD 934. Thecardioversion/defibrillation energy can be delivered between the activesurface of the device housing and electrodes on each lead. The desiredelectrodes for sensing and/or shocking can be selected by the device. Aneural stimulation lead 940 extends from the device 934 to a vagaltarget. The neural stimulation lead 940 can be tunneled subcutaneouslyto the vagus nerve, or can be transvascularly fed to the internaljugular vein adjacent to the vagus nerve. Satellite electrodes may beused to deliver neural stimulation.

FIG. 10 illustrates an embodiment of a system, including a subcutaneousICD 1037 and an implantable vagal nerve stimulator 1036. The ICD 1037has subcutaneous leads 1039A and 1039B similar to the leads 939A and939B described with respect to FIG. 9. A separate vagal nerve stimulator1036 includes a neural stimulation lead 1040, which can be tunneledsubcutaneously to the vagus nerve, or can be transvascularly fed to theinternal jugular vein adjacent to the vagus nerve. The ICD and nervestimulator are adapted to communicate with each other. The illustratedsystem illustrates wireless communication between the devices, such asmay be achieved using ultrasound or radiofrequency signals. Asubcutaneously tunneled tether can connect the two implanted devices,and communication and/or power can be provided through the tether. Thus,the neural stimulation to lower the DFT can be coordinated with thedelivery of the subcutaneous defibrillation.

FIG. 11 illustrates an embodiment of a subcutaneous ICD with vagal nervestimulation. The illustrated ICD 1134 provides vagal nerve stimulationusing satellite electrodes 1141. The satellite electrode can include itsown power, and can wirelessly communicate with the ICD. The satelliteelectrodes can include nerve cuff electrodes, transvascular electrodes,and subcutaneous electrodes. The subcutaneous ICD 1134 may be used inadults where chronic transvenous/epicardial ICD lead systems poseexcessive risk or have already resulted in difficulty such as sepsis orlead fractures, and may be used for use in children whose growth posesproblems with transvenous ICDs. FIG. 11 also illustrates the placementof the subcutaneous lead 1139, which is fed in a serpentine fashionrather than a taught configuration. As the child grows, the bends in thelead straighten allowing the proper electrode placement to bemaintained. An anchor can be used to fix the distal end of the lead.

FIG. 12 is a block diagram illustrating an embodiment of an externalsystem 1242. The external system includes a programmer, in someembodiments. In the embodiment illustrated in FIG. 12, the externalsystem includes a patient management system. As illustrated, externalsystem 1242 is a patient management system including an external device1243, a telecommunication network 1244, and a remote device 1245. Theexternal device 1243 is placed within the vicinity of an IMD andincludes external telemetry system 1246 to communicate with the IMD.Remote device(s) 1245 is in one or more remote locations andcommunicates with the external device 1243 through the network 1244,thus allowing a physician or other caregiver to monitor and treat apatient from a distant location and/or allowing access to varioustreatment resources from the one or more remote locations. Theillustrated remote device 1245 includes a user interface 1247.

In various embodiments, the vagal nerve stimulation is applied to reducethe DFT for an antitachycardia shock delivering through subcutaneousand/or intracardiac electrodes. In various embodiments, in addition todelivering neural stimulation in preparation for an antitachycardiashock as discussed above, one or more other techniques are used tofurther lower the DFT. For illustrative purposes, embodiments of suchother techniques are discussed below with reference to FIGS. 13-15. Inthese embodiments, various configurations of intracardiac electrodes arediscussed as specific examples. However, the present subject matterapplies to delivery of an antitachycardia shock through intracardiac,subcutaneous, or external electrodes, or various combinations of theseelectrodes. In general, any two or more of the methods and devices forthe vagal nerve stimulation and for other techniques for lowering theDFT may be combined to reduce or minimize the energy required toterminate a tachyarrhythmic episode.

FIG. 13 illustrates an embodiment of an IMD 1348 with an intracardiaclead system for delivering an anti-arrhythmic therapy. In variousembodiments, IMD 1348 represents any IMD that includes ICD functions ora combination of NS and ICD functions, where the NS functions providefor lowering of the DFT. Examples of IMD 1348 include devices 534, 637,734, 837,934, 1037, and 1134 discussed above. The lead system includesimplantable intracardiac leads 1350, 1355, and 1365.

IMD 1348 includes a hermetically sealed can housing an electroniccircuit that senses physiological signals and delivers therapeuticelectrical pulses. The hermetically sealed can also functions as a canelectrode 1349 for sensing and/or pulse delivery purposes. In variousembodiments, in addition to the NS and ICD functions, IMD 1348 performsone or more other monitoring and/or therapeutic functions such as drugdelivery and biologic therapy delivery functions. In one embodiment, adrug therapy or biologic therapy is delivered to further reduce the DFT.

Lead 1350 is a right atrial (RA) pacing lead that includes an elongatelead body having a proximal end 1351 and a distal end 1353. Proximal end1351is coupled to a connector for connecting to IMD 1348. Distal end1353 is configured for placement in the RA in or near the atrial septum.Lead 1350 includes an RA tip electrode 1354A, and an RA ring electrode1354B. RA electrodes 1354A and 1354B are incorporated into the lead bodyat distal end 1353 for placement in or near the atrial septum, and areeach electrically coupled to IMD 1348 through a conductor extendingwithin the lead body. RA tip electrode 1354A, RA ring electrode 1354B,and/or can electrode 1349 allow for sensing an RA electrogram indicativeof RA depolarizations and delivering RA pacing pulses.

Lead 1355 is a right ventricular (RV) pacing-defibrillation lead thatincludes an elongate lead body having a proximal end 1357 and a distalend 1359. Proximal end 1357 is coupled to a connector for connecting toIMD 1348. Distal end 1359 is configured for placement in the RV. Lead1355 includes a supraventricular defibrillation electrode such as asuperior vena cava (SVC) defibrillation electrode 1356, an RVdefibrillation electrode 1358, an RV tip electrode 1360A, and an RV ringelectrode 1360B. SVC defibrillation electrode 1356 is incorporated intothe lead body in a location suitable for supraventricular placement inthe SVC and/or the RA. RV defibrillation electrode 1358 is incorporatedinto the lead body near distal end 1359 for placement in the RV. RVelectrodes 1360A and 1360B are incorporated into the lead body at distalend 1359. Electrodes 1356, 1358, 1360A, and 1360B are each electricallycoupled to IMD 1348 through a conductor extending within the lead body.SVC defibrillation electrode 1356, RV defibrillation electrode 1358,and/or can electrode 1349 allow for delivery ofcardioversion/defibrillation pulses to the heart. RV tip electrode1360A, RV ring electrode 1360B, and/or can electrode 1349 allow forsensing an RV electrogram indicative of RV depolarizations anddelivering RV pacing pulses.

Lead 1365 is a left ventricular (LV) coronary pacing-defibrillation leadthat includes an elongate lead body having a proximal end 1361 and adistal end 1363. Proximal end 1361 is coupled to a connector forconnecting to IMD 1348. Distal end 1363 is configured for placement inthe coronary vein (as illustrated) or the coronary sinus. Lead 1365includes one or more LV pacing and/or defibrillation electrodes forplacement along the coronary sinus and/or the coronary vein over the LV.Examples of such LV electrodes as illustrated in FIG. 13 include acoronary sinus (CS) electrode 1369 and a coronary vein (CV) electrode1368. CS electrode 1369 and CV electrode 1368 are each electricallycoupled to IMD 1348 through a conductor extending within the lead body.In various embodiments, CS electrode 1369, CV electrode 1368 and/or thecan electrode 1349 allow for sensing an LV electrogram indicative of LVdepolarizations and delivering LV pacing pulses. In various embodiments,electrodes selected from CS electrode 1369, CV electrode 1368, SVCdefibrillation electrode 1356, RV defibrillation electrode 1358, and/orcan electrode 1349 allow for delivery of antitachycardia shocks to theheart.

CS electrode 1369, CV electrode 1368, SVC defibrillation electrode 1356,and RV defibrillation electrode 1358 are specific examples of electrodes422A, 422B, and 422C, and can electrode 1349 is a specific example ofcan electrode 426. The leads and electrodes in FIG. 13 are forillustrative purposes only. Other lead configurations may be used,depending on monitoring and therapeutic requirements. For example,additional leads may be used to provide access to additional cardiacregions, and leads 1350, 1355, and 1365 may each include more or fewerelectrodes along the lead body at, near, and/or distant from the distalend, depending on specified monitoring and therapeutic needs.

FIG. 14 illustrates an embodiment of an antitachycardia shock waveformthat includes a biphasic pulse. One electrode system for delivering anantitachycardia shock with such a waveform includes SVC defibrillationelectrode 1356, RV defibrillation electrode 1358, and can electrode1349. For example, RV defibrillation electrode 1358 is used as thecathode, and SVC defibrillation electrode 1356 and can electrode 1349are electrically wired to be used as the anode, for the shock delivery.The addition of at least one of the LV electrodes (CS electrode 1369 andCV electrode 1368) to this electrode system will lower the DFT. In oneembodiment, RV defibrillation electrode 1358 is used as the cathode, andSVC defibrillation electrode 1356, at least one of the CS electrode 1369and CV electrode 1368, and can electrode 1349 are electrically wired tobe used as the anode, for delivering a ventricular defibrillation shock.In another embodiment, RV defibrillation electrode 1358 and at least oneof the CS electrode 1369 and CV electrode 1368 are electrically wired tobe used as the cathode, and SVC defibrillation electrode 1356 and canelectrode 1349 are electrically wired to be sued as the anode, fordelivering a ventricular defibrillation shock. In another embodiment, CSdefibrillation electrode 1369 is used as the cathode, and SVCdefibrillation electrode 1356 and can electrode 1349 are electricallywired to be used as the anode, for delivering an atrial defibrillationshock. In each of these embodiments, the polarity may be reversed.

FIG. 15 illustrates another embodiment of an antitachycardia shockwaveform that includes multiple pulses for each single shock. Using ashock waveform including multiple pulses will lower the DFT. In theillustrated embodiment, the antitachycardia shock waveform includes amonophasic auxiliary pulse followed by a biphasic primary pulse. Theprimary pulse is delivered through a primary electrode set along acurrent pathway in a portion of the heart. The auxiliary pulse isdelivered through an auxiliary electrode set to another portion of theheart where the current intensity resulting from the primary pulse is ator near a minimum. In various embodiments, the primary electrode setdiffers from the auxiliary electrode set by at least one electrode.

In one embodiment, the primary electrode set and the auxiliary electrodeset each include electrodes selected from SVC defibrillation electrode1356, RV defibrillation electrode 1358, the LV electrodes (CS electrode1369 and CV electrode 1368), and can electrode 1349.

In one embodiment, CS electrode 1369 is used as the cathode fordelivering the auxiliary pulse, can electrode 1349 is used as the anodefor delivering the auxiliary pulse, SVC defibrillation electrode 1356 isused as the cathode for delivering the primary pulse, and RVdefibrillation electrode 1358 is used as the anode for delivering theprimary pulse.

In another embodiment, SVC defibrillation electrode 1356 is used as thecathode for delivering the auxiliary pulse, RV defibrillation electrode1358 is used as the anode for delivering the auxiliary pulse, CSelectrode 1369 is used as the cathode for delivering the primary pulse,and can electrode 1349 is used as the anode for delivering the primarypulse.

In another embodiment, CS electrode 1369 is used as the cathode fordelivering the auxiliary pulse, SVC defibrillation electrode 1356 isused as the anode for delivering the auxiliary pulse, RV defibrillationelectrode 1358 is used as the cathode for delivering the primary pulse,and CS electrode 1369 is also used as the anode for delivering theprimary pulse.

In another embodiment, RV defibrillation electrode 1358 is used as thecathode for delivering the auxiliary pulse, can electrode 1349 is usedas the anode for delivering the auxiliary pulse, CS electrode 1369 isused as the cathode for delivering the primary pulse, and SVCdefibrillation electrode 1356 is used as the anode for delivering theprimary pulse.

In another embodiment, CS electrode 1369 is used as the cathode fordelivering the auxiliary pulse, can electrode 1349 is used as the anodefor delivering the auxiliary pulse, RV defibrillation electrode 1358 isused as the cathode for delivering the primary pulse, and can electrode1349 is used as the anode for delivering the primary pulse.

In another embodiment, CS electrode 1369 is used as the cathode fordelivering the auxiliary pulse, RV defibrillation electrode 1358 is usedas the anode for delivering the auxiliary pulse, RV defibrillationelectrode 1358 is also used as the cathode for delivering the primarypulse, and SVC defibrillation electrode 1356 and can electrode 1349 areelectrically wired to be used as the anode for delivering the primarypulse.

In another embodiment, RV defibrillation electrode 1358 is used as thecathode for delivering the auxiliary pulse, CS electrode 1369 is used asthe anode for delivering the auxiliary pulse, RV defibrillationelectrode 1358 and CS electrode 1369 are electrically wired to be usedas the cathode for delivering the primary pulse, and SVC defibrillationelectrode 1356 and can electrode 1349 are electrically wired to be usedas the anode for delivering the primary pulse.

In another embodiment, CS electrode 1369 is used as the cathode fordelivering the auxiliary pulse, can electrode 1349 is used as the anodefor delivering the auxiliary pulse, RV defibrillation electrode 1358 andCS electrode 1369 are electrically wired to be used as the cathode fordelivering the primary pulse, and SVC defibrillation electrode 1356 andcan electrode 1349 are electrically wired to be used as the anode fordelivering the primary pulse.

In another embodiment, CS electrode 1369 is used as the cathode fordelivering the auxiliary pulse, can electrode 1349 is used as the anodefor delivering the auxiliary pulse, RV defibrillation electrode 1358 isused as the cathode for delivering the primary pulse, and CS electrode1369, SVC defibrillation electrode 1356, and can electrode 1349 areelectrically wired to be used as the anode for delivering the primarypulse.

In one embodiment, the primary pulse has a primary pulse width in therange of 0.5 to 20 milliseconds, the auxiliary pulse has an auxiliarypulse width in the range of 0.5 to 10 milliseconds, and the primarypulse and the auxiliary pulse are separated by an interpulse delay inthe range of 0 to 20 milliseconds. In one embodiment, one or more of theprimary pulse width, the auxiliary pulse width, and the interpulse delayare programmable.

The electrode configurations and waveforms for the antitachycardia shockdiscussed in this document are specific examples. In variousembodiments, the electrode system for delivering the antitachycardiashock may include intracardiac electrodes, epicardial electrodes,subcutaneous electrodes, and any combination thereof; and the waveformof the antitachycardia shock may include one or more pulses and/orphases. Examples of such electrode configurations and waveforms are alsodiscussed in U.S. Pat. No. 5,107,834, entitled “LOW ENERGY MULTIPLESHOCK DEFIBRILLATION/CARDIOVERSION DISCHARGE TECHNIQUE AND ELECTRODECONFIGURATION”, assigned to Cardiac Pacemakers, Inc., U.S. Pat. No.5,540,723, entitled “METHOD AND APPARATUS FOR DELIVERING AN OPTIMUMSHOCK DURATION IN TREATING CARDIAC ARRHYTHMIAS”, assigned to DukeUniversity and Cardiac Pacemakers, Inc., U.S. Pat. No. 5,603,732,entitled “SUBCUTANEOUS DEFIBRILLATION ELECTRODES”, assigned to CardiacPacemakers, Inc., U.S. Pat. No. 5,978,705, entitled “METHOD ANDAPPARATUS FOR TREATING CARDIAC ARRHYTHMIA USING AUXILIARY PULSE,”assigned to UAB Research Foundation, U.S. Pat. No. 6,002,962, entitled“IMPLANTABLE TRIPHASIC WAVEFORM DEFIBRILLATOR”, assigned to UAB ResearchFoundation, and U.S. patent application Ser. No. 11/275,943, entitled“METHOD AND APPARATUS FOR TERMINATION OF CARDIAC TACHYARRHYTHMIAS”,assigned to Cardiac Pacemakers, Inc., filed on Feb. 6, 2006, which areincorporated herein by reference in their entirety. Other waveforms andelectrode configurations are possible as determined by those of ordinaryskill in the art upon reading and understanding this document. Invarious embodiments, microprocessor 420 controls the electrodeconfiguration and the waveform for each delivery of the antitachycardiashock. In one embodiment, either of both of the electrode configurationand the waveform for the antitachycardia shock is programmable by a userthrough external system 1242.

In various embodiments, in response to the detection of a specifiedcardiac activity indicated for an antitachycardia shock, vagal nervestimulation is delivered for a neurostimulation period before theantitachycardia shock is delivered. In one embodiment, theneurostimulation period is between 1 second and 20 seconds. In oneembodiment, the neurostimulation period is programmable, such as by auser through external system 1242. In various embodiments, theantitachycardia shock that follows the vagal nerve stimulation has awaveform as illustrated in FIG. 14 or FIG. 15 or any other knowncardioversion/defibrillation waveform. In one embodiment, microprocessor420 initiates and times the neurostimulation period and initiates thedelivery of the antitachycardia shock upon expiration of theneurostimulation period. In one embodiment, microprocessor 420 initiatesthe delivery of the antitachycardia shock upon expiration of theneurostimulation period only if the specified cardiac activity sustainsat the end of the neurostimulation period.

The methods illustrated in this disclosure are not intended to beexclusive of other methods within the scope of the present subjectmatter. Those of ordinary skill in the art will understand, upon readingand comprehending this disclosure, other methods within the scope of thepresent subject matter. The above-identified embodiments, and portionsof the illustrated embodiments, are not necessarily mutually exclusive.These embodiments, or portions thereof, can be combined. In variousembodiments, the methods provided above are implemented as a computerdata signal embodied in a carrier wave or propagated signal, thatrepresents a sequence of instructions which, when executed by aprocessor cause the processor to perform the respective method. Invarious embodiments, methods provided above are implemented as a set ofinstructions contained on a computer-accessible medium capable ofdirecting a processor to perform the respective method. In variousembodiments, the medium is a magnetic medium, an electronic medium, oran optical medium. One of ordinary skill in the art will understand thatthe modules and other circuitry shown and described herein can beimplemented using software, hardware, and combinations of software andhardware.

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat any arrangement which is calculated to achieve the same purpose maybe substituted for the specific embodiment shown. This application isintended to cover adaptations or variations of the present subjectmatter. It is to be understood that the above description is intended tobe illustrative, and not restrictive. Combinations of the aboveembodiments as well as combinations of portions of the above embodimentsin other embodiments will be apparent to those of skill in the art uponreviewing the above description. The scope of the present subject mattershould be determined with reference to the appended claims, along withthe full scope of equivalents to which such claims are entitled.

1. A system configured to be coupled to a heart including a right atrium(RA) connected to a superior vena cava (SVC), a right ventricle (RV), aleft ventricle (LV), a coronary sinus, and a coronary vein, the systemcomprising: a sensor configured to detect a cardiac activity indicatedfor a defibrillation shock; a vagal nerve stimulator configured todeliver vagal nerve stimulation to lower a defibrillation threshold inpreparation for delivering the defibrillation shock; a plurality ofdefibrillation electrodes including at least one LV electrode configuredto be placed in the coronary sinus or coronary vein; and a defibrillatorconfigured to deliver the defibrillation shock to the heart through theplurality of defibrillation electrodes.
 2. The system of claim 1,comprising an implantable housing configured to house both the vagalnerve stimulator and the defibrillator.
 3. The system of claim 1,comprising a first implantable housing configured to house the vagalnerve stimulator and a second implantable housing configured to housethe defibrillator.
 4. The system of claim 1, comprising a controllerconfigured to initiate and time a neurostimulation period in response tothe detection of the cardiac activity, and wherein the vagal nervestimulator is configured to deliver the vagal nerve stimulation duringthe neurostimulation period.
 5. The system of claim 4, wherein thecontroller is configured to initiate the delivery of the defibrillationshock in response to an expiration of the neurostimulation period. 6.The system of claim 5, wherein the controller is configured to initiatethe delivery of the defibrillation shock if the cardiac activity remainsdetected at the end of the neurostimulation period.
 7. The system ofclaim 4, wherein the controller is configured to control a waveform ofthe defibrillation shock, the waveform including a plurality of pulses.8. The system of claim 7, wherein the controller is configured tocontrol a waveform of the defibrillation shock, the waveform includingan auxiliary pulse followed by a primary pulse.
 9. The system of claim8, wherein the controller is configured to time an interpulse intervalbetween the auxiliary pulse and the primary pulse.
 10. The system ofclaim 8, comprising a plurality of electrodes coupled to thedefibrillator, the plurality of electrodes including: an auxiliaryelectrode set through which the auxiliary pulse is delivered; and aprimary electrode set through which the primary pulse is delivered,wherein the auxiliary electrode set is different from the primaryelectrode set by at least one electrode.
 11. The system of claim 1,comprising an implantable housing and a plurality of electrodes, theimplantable housing configured to house at least the defibrillator, theplurality of electrodes coupled to the defibrillator and including: theat least one LV electrode; a supraventricular defibrillation electrodeconfigured to be placed in one or more of the SVC and the RA; an RVdefibrillation electrode configured to be placed in the RV; and a canelectrode including at least a portion of the implantable housing. 12.The system of claim 11, wherein the plurality of electrodes areconnected to the defibrillator such that the RV defibrillation electrodeis used as a cathode for delivering the defibrillation shock, and the atleast one LV electrode, the SVC defibrillation electrode, and the canelectrode are electrically wired to be used as an anode for deliveringthe defibrillation shock.
 13. The system of claim 11, comprising a leadincluding a primary end, a distal end, and an elongate body coupledbetween the primary end and the distal end, the primary end configuredto be coupled to the defibrillator, the distal end including the atleast one LV electrode, the lead configured to allow the distal end tobe placed in the coronary sinus.
 14. The system of claim 11, comprisinga lead including a primary end, a distal end, and an elongate bodycoupled between the primary end and the distal end, the primary endconfigured to be coupled to the defibrillator, the distal end includingthe at least one LV electrode, the lead configured to allow the distalend to be placed in the coronary vein.
 15. A method for defibrillating aheart including a right atrium (RA) connected to a superior vena cava(SVC), a right ventricle (RV), a left ventricle (LV), a coronary sinus,and a coronary vein, comprising: detecting a cardiac activity indicatedfor a defibrillation shock; applying neural stimulation to lower adefibrillation threshold in preparation for the defibrillation shock;and delivering the defibrillation shock using a plurality ofdefibrillation electrodes including at least one LV electrode placed inthe coronary sinus or coronary vein.
 16. The method of claim 15,comprising: initiating and timing a neurostimulation period in responseto the detection of the cardiac activity; and delivering a vagal nervestimulation during the neurostimulation period.
 17. The method of claim16, comprising establishing the neurostimulation period to a periodbetween 1 second and 20 seconds.
 18. The method of claim 16, comprisinginitiating the delivery of the defibrillation shock in response to anexpiration of the neurostimulation period.
 19. The method of claim 18,comprising initiating the delivery of the defibrillation shock if thecardiac activity sustains at the end of the neurostimulation period. 20.The method of claim 15, wherein delivering the defibrillation shockcomprises delivering a defibrillation shock having a waveform includinga plurality of pulses.
 21. The method of claim 20, wherein deliveringthe defibrillation shock having the waveform including the plurality ofpulses comprises delivering a defibrillation shock having a waveformincluding an auxiliary pulse followed by a primary pulse, and whereindelivering the defibrillation shock using the plurality ofdefibrillation electrodes comprises delivering the auxiliary pulse usingan auxiliary electrode set and delivering the primary pulse using aprimary electrode set, the auxiliary electrode set different from theprimary electrode set by at least one electrode.
 22. The method of claim21, comprising controlling an interpulse interval between the auxiliarypulse and the primary pulse.
 23. The method of claim 22, comprisingsetting the interpulse interval to a time interval between 0 and 20milliseconds.
 24. The method of claim 15, wherein delivering thedefibrillation shock using the plurality of defibrillation electrodescomprises using the at least one LV electrode, a supraventriculardefibrillation electrode placed in one or more of the SVC and the RA, anRV defibrillation electrode placed in the RV, and a can electrodeincluding at least a portion of an implantable housing configured tohouse at least a defibrillator from which the defibrillation isdelivered.
 25. The method of claim 24, wherein delivering thedefibrillation shock using the plurality of defibrillation electrodescomprises: using the RV defibrillation electrode as a cathode; and usingthe at least one LV electrode, the SVC defibrillation electrode, and thecan electrode as an anode, the at least one LV electrode, the SVCdefibrillation electrode, and the can electrode electrically wired toeach other.
 26. The method of claim 24, wherein using the at least oneLV electrode comprises using an electrode placed in the coronary sinus.27. The method of claim 24, wherein using the at least one LV electrodecomprises using an electrode placed in the coronary vein.
 28. A systemcoupled to a heart including a right atrium (RA) connected to a superiorvena cava (SVC), a right ventricle (RV), a left ventricle (LV), acoronary sinus, and a coronary vein, the system comprising: means fordetecting a cardiac activity indicated for a defibrillation shock; meansfor applying neural stimulation to lower a defibrillation threshold inpreparation for the defibrillation shock; and means for subcutaneouslydelivering the defibrillation shock using a plurality of defibrillationelectrodes including at least one LV electrode placed in the coronarysinus or coronary vein.